This study will address the problem of detection, identification and control of Giardia strains which are significant to waterborne transmission of giardiasis in public water supplies. The protozoan parasite Giardia lamblia is of acknowledged significance as a waterborne etiologic agent requiring control to maintain the safety of public water supplies. In many of the waterborne giardiasis outbreaks, Giardia infected mammals, most notable the beaver, have been implicated as the probable source. However, the source of the infective Giardia strains the waterborne outbreaks has never rigorously established, nor has it been possible to determine which species of animal(s) (if any) contributexd to the human infective cysts. We will adopt into axenic culture 150 new isolates of Giardia collected in equal numbers from humans in the Seattle-Tacoma area and from animals inhabiting three watersheds serving the SeattleTacoma area. These, with our existing collection of 30 isolates and 20 to be sought from other investigators will be used to determine the range of unique isolates relative to the total and to examine the correspondence between isolates found in the watershed and in the community served by the water supply. Isolates will be characterized and differentiated using RFLP and Southern blotting, using homologous and nonhomologous rRNA probes and using Giardia genomic DNA probes from our G. lamblia genomic library (in pUC8). The problrm of identifying by type Giardia cysts found at very low concentration in sources of public water supply be addressed by developing immunological reagents specific to Giardia isolate groups of interest. Unique and common antigens of individual isolates an isolate groups will be identified by Western blotting probed with our existing battery of 30 monoclonal, two monospecific, and three polyclonal antibodies. Additional monospecific and/or monoclonal antibodies may be developed if needed. Requirements for control of G. lamblia cysts in public water supply will be addressed by establishing the disinfection characteristics of cysts from isolates representative of the range of isolate types identified in other parts of the project.